1. Field of the Invention
The present invention relates to an imprint method, imprint apparatus, and article manufacturing method.
2. Description of the Related Art
The imprint technique is a technique that makes transfer of nanoscale micropatterns possible, and is beginning to be put into practical use as one nanolithography technique for the mass-production of magnetic recording media and semiconductor devices. An apparatus such as an electron-beam exposure apparatus is used to form, on the mesa surface of a mold, patterns of a shot region to be transferred by the imprint technique. A mold having patterns formed by using an apparatus such as an electron-beam exposure apparatus is imprinted as an original on a substrate such as a silicon wafer or glass plate as a pattern transfer target, thereby transferring the patterns. These micropatterns are formed by coating the substrate with an imprinting resin (dispensing the resin on the substrate), and curing the resin while the patterns of the mold are pressed against the substrate with the resin being sandwiched between them.
Imprint techniques presently put into practical use are the heat cycle method and photo-curing method. In the heat cycle method, while the fluidity of a thermoplastic resin is increased by heating the resin to a temperature equal to or higher than the glass-transition temperature, a mold is pressed against a substrate with the resin being sandwiched between them. After the resin is cooled, patterns are formed on the resin by releasing the mold from the resin. On the other hand, the photo-curing method uses an ultraviolet-curing resin. While a mold made of a light-transmitting material such as quartz is pressed against a resin dispensed on the substrate, the resin is cured by ultraviolet irradiation, and patterns are formed on the cured resin by releasing the mold from the resin. In the heat cycle method, the transfer time increases due to temperature control, and the dimensional accuracy and positional accuracy decrease due to a temperature change. However, the photo-curing method has no such problems. Therefore, the photo-curing method is advantageous in the mass-production of nanoscale semiconductor devices.
Various imprint apparatuses have been implemented in accordance with resin curing methods and applications. As an apparatus for mass-producing semiconductor devices and the like, an apparatus using jet and flash imprint lithography (JFIL) is effective. An imprint apparatus fitted for JFIL is disclosed in Japanese Patent Laid-Open No. 2009-266841. This imprint apparatus includes a substrate stage, resin coating mechanism, imprint head, light irradiation system, and positioning alignment mark detecting mechanism. The apparatus uses a step-and-repeat method as in an exposure apparatus because the area of a shot region to be imprinted by one imprint operation is limited.
As an application of the imprint technique to semiconductors, a first possible application is to memory elements. The problem of memory elements is to reduce the cost by mass-production, and the most effect method of cost reduction is micropatterning. As is well known, the imprint technique is highly capable of micropatterning, and best suited to the need of memory elements. A defect of imprint processing is a high risk of decreasing the yield of semiconductor production. Examples of mold defects are a mold break caused by a particle adhered on a wafer, and clogging that occurs if a cured resin partially remains on a mold when the mold is released from the resin. These mold defects continuously cause transfer defects on following shot regions to be imprinted (repetitive defects). Accordingly, it is very important to analyze cases in which these mold defects occur, and remove the defects in accordance with the main causes. Japanese Patent Laid-Open No. 2009-266841 has proposed a method of coating a dummy wafer with a particle removing film having high adhesion to a light-curing resin, coating the particle removing film with a light-curing resin, and performing imprinting, thereby removing particles adhered to a mold by incorporating the particles into the light-curing resin. Also, Japanese Patent Laid-Open No. 2010-69762 has disclosed a method by which if a foreign substance that may break a mold is found on a wafer by inspecting the presence/absence of a foreign substance, imprint processing is performed on a shot region including the foreign substance by switching a mold to a dummy mold for which imprint processing can be performed.
Presently, however, even when a foreign substance such as a particle on a wafer can be found by an inspection apparatus beforehand, there is no method of removing the foreign substance. Therefore, it is necessary to perform imprint processing by using a dummy mold as disclosed in Japanese Patent Laid-Open No. 2010-69762, or perform no imprint processing on a shot region where the foreign substance exists. In the method using a dummy mold, it is difficult to form normally functioning circuit patterns, but the film thickness after imprinting is maintained. Accordingly, no adverse effect is given to surrounding shot regions during etching. However, it is necessary to use another mold support for holding the dummy mold, or switch the molds. This increases the apparatus cost or decreases the productivity. On the other hand, when no imprint processing is performed on a shot region where the foreign substance exists, an adverse effect may be given to shot regions normally imprinted in a subsequent etching process. Furthermore, neither methods can produce usable chips from shot regions imprinted by using the dummy mold, or from shot regions that are not imprinted. That is, no usable chip can be produced even from a chip region having no foreign substance problem, and this decreases the chip yield.